1. Field of the Invention
This invention lies in the field of artificial fractures in the earth resulting from the application of fluid pressure, at a selected point, at a selected depth, in the earth, in a selected geologic formation, of selected properties.
More particularly this invention is related to the mapping of such fractures, that is, determining the horizontal shape and size of the outer perimeter of the fractures.
2. Background of the Invention
In the petroleum industry over the past 25 years or so, it has been customary to artificially create fractures in the earth by means of fluid pressure applied at selected points in the earth. These processes have come to be known as hydrofracturing, or hydrofraccing, since liquids were the first fluids to be used. Liquids are still used in forming deep vertical fractures, where very high pressures are required.
On the other hand, where the hydrocarbon containing formation is shallow, and the fractures are horizontal, air or steam can be used to create the fractures, such as when creating fractures in shallow tar sands, for example.
However, in all the years that such artificial fracturing has been done, no satisfactory way has been found to precisely determine the azimuth, length and vertical extent of a deep vertical fracture, or the shape and dimension of the outer perimeter of a horizontal fracture.
In a related application, filed on the same date as this application, by M. Darroll Wood, entitled: Method of Determining Change in Subsurface Structure Due to Application of Fluid Pressure to the Earth, he has described a method of positioning tiltmeters on the surface of the earth over the expected position of the fracture, and by observing the variation of tilt of the earth, as a function of the pressure and flow rate of liquid into a deep vertical fracture, he is able to determine the azimuth of, and the horizontal extent of, the deep vertical fracture.
To applicant's knowledge, no other method has been described in the literature, for mapping artificial fractures in the earth.